Human cytomegalovirus (HCMV), a β-herpesvirus, is a ubiquitously occurring pathogen. In an immunocompetent person, HCMV infection is normally unnoticed, having at most mild and nonspecific symptoms. By contrast, certain risk groups, for example in immunosuppressed patients such as AIDS patients or transplant recipients, and after prenatal infection, HCMV infection has serious manifestations (Staras S A et al., 2006 Clin Infect Dis 43(9):1143-51; Hebart H et al., 2004 Hum Immunol 65(5):432-6; Rowshani A T et al., 2005 Transplantation 79(4):381-6). Existing therapies include the use of immunoglobulins and anti-viral agents such as ganciclovir and its derivatives, which are most effective when used prophylactically or very early during infection in at risk populations. However, existing therapies are characterized by significant toxicity and limited efficacy, especially for late-onset disease (Boeckh M., 2004 Pediatr Transplant 8(Suppl. 5):19-27; Limaye A P., 2004 Transplantation 78(9):1390-6), and they have not had an impact on congenital HCMV disease. Development of an effective vaccine to protect against HCMV disease is recognized as an important public health priority (Arvin A M et al., 2004 Clin Infect Dis 39(2):233-9).
In vitro assays are important tools to evaluate candidate vaccines for their ability to interfere with HCMV infection. For example, neutralization assays have been developed to study immune responses in infected individuals as well as to assess vaccine immunogen candidates in both clinical and preclinical trials. In the case of HCMV, antigen binding ELISAs can measure antibodies specific for HCMV antigens; however, only an assay in which neutralization of viral entry into cells is measured can establish and quantify the biological activity of HCMV antigen-specific antibodies (Abai et al., 2007 J Immunol Methods 332(1-2):82-93). Typically, in such neutralization assays for HCMV, the degree to which neutralizing antibodies reduce HCMV infection of cells in the assay is determined by quantification of nuclei of infected cells based on expression of one or more viral proteins in the cell. Such analyses can be time consuming and difficult to employ in high throughput applications. There remains a need in the art for improved methods of screening potential HCMV vaccine candidates for neutralizing antibody induction.